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Feb. 16, 1954 WEAVER r Re. 23,784

BALANCE TESTING APPLIANCE Original Filed Sept. 21, 1945 6 Sheets-Sheet L Feb. I6, 1954 1. A. WEAVER EI'AL BALANCE TESTING APPLIANCE 6 Sheets-Sheet 2 Original Filed Sept. 21, 1945 Feb. 16, 1954 LA. WEAVER ETAL Re. 23,784

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Feb. 16, 1954 l. A. WEAVER ETAL BALANCE TESTING APPLIANCE Original Filed Sept. 21, 1945 6 Sheets-Sheet 6 AAAAA vvvvvv INVENTORS .1710 d. Weaver Reiseued Feb. 16, 1954 BALANCE TESTING APPLIANCE in A. Weaver and case n.

111., assignors, by mesne Machine Company, Madison, Wis., a corporation of Wisconsin rum. Sprin fiel assignments, to Gisholt No."2,486.896, dated November 1, 1949, Serial No. 617,772, September 21, 1945. Application for reissue October 30, 1950, Serial No.

17 Claims.

The present invention relates to certain features of betterment and advantage in balancetesting machines for rotors of various types whereby to determine the amount and location of the unbalance present preliminary to its elimination.

The invention has several objects among which may be mentioned the provision of a construction which functions eil'ectively and efllciently and which may be actuated with ease and facility, accuracy and reliability of results being an important factor, as well as simplicity in structure and moderate cost of production.

To enable'those skilled in this art to readily understand the invention and the advantages accruing from its employment, 9. present preferred embodiment thereof has been illustratedin detail in the accompanying drawings, forming a part of the specification, and to which reference should be had in connection with the following description, like reference numerals having been employed throughout the several views of the drawings to designate the same parts or.

elements.

In these drawings:

Figure 1 is a front elevation of the appliance;

Figure 2 is a plan view of the same;

Figure 3 is an elevation of the right-hand end of the structure;

Figure 4 is a plan or face view of the unbalance indicator;

Figure 5 is a vertical section on line 5-5 of Figure 4;

Figure 6 is an end elevation of presented in Figure 4; and

Figure 'l is a diagram of the electric circuits and the elements included therein.

Referring to Figures 1, 2 and 3 of the drawings, it will be noted that the machine for supporting and revolving the rotor II to be tested as to its dynamic balance or lack thereof may comprise a stationary, horizontal frame 22 supported on end members II, ll connected together at their lower portions by a pair of parallel rods II, 24 on which is mounted an electric-motor 25 whose pulley 2| rotates the rotor II by means of the belt 21 connecting therewith.

Such rotor ii is mounted on and revolves with its shaft I8. whose end portions are rotatable in a pair of bearing-members 29, 19 each supported from above by two depending wires 8 I, 3| secured at their upper ends to supports 32, 32 upstanding from the terminal portions of frame 22, whereby these bearing-members and their shaft 28 and rotor 2| are free to vibrate or oscillate in their horizontal plane.

the indicator Matter enclosed in heavy brackets I: II appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made byreissue.

One of the pair of bearing-members 29, in the present case the right-hand one, is equipped with oppositely-facing twin standards or brackets 53. 34 (Figure 3) fixedly secured thereto and therefore movable or vibratory therewith in any horizontal direction.

On the flat, top, horizontal surface of each such bracket 33, 84 is firmly mounted a vibration-actuated balance-indicator (Figures 4, 5 and 6) including a frame comprising four, shouldered posts 35' screw-threaded at their lower ends at 35 which extend through complementary holes in the bracket and have securing nuts 31 on such ends, these posts coniointly carrying a flat topplate 38 and a larger, lower, apertured bent plate 39.

The hub (Fig. 5), on which a gear-sector 42 is fixed has longitudinally spaced'apart, vertical pivots l3 and It pressed fixedly into the end portions of gear-hub aperture 45, the conical ends of such registered pivots being accommodated in bearings Iii and 41 mounted on plates 38 and 39.

An elongated, horizontal, screw-threaded rod 48 fits in, extends through, and is adjustable lengthwise in, a screw-threaded hole through the hub Ii between the adjacent ends of the two pivots 43, 44 (Figs. 4, 5 and 6), such rod on opposite sides of the hub carrying two inertia masses or weights 49 and 5| (Figs. 4 and of different values threaded on, and therefore individually longitudinally adjustable on, the rod, .the latter being held in place by a set-screw 52 engaging it in the gear-hub ll (Figs. 5 and 6), each weight 49 and 5| having its own set-screw 53 (Figs. 4 and 6) for maintenance of its lengthwise adjustment on the rod.

The inner end of a coiled-spring 54 (Figs. 4 and 5) is secured to a member 55 mounted on the upper pivot ll (Fig. 5), the outer end of such spring being adjustably connected to a member 56 depending from the friction-controlled part 51 (Figs. 4 and 5) adjustable angularly around the axis of bearing 45 to vary the tension of the spring.

Analogously, the inner end of an oppositely coiled spring 58 is connected to the lower pivot 44 by a member 59, the outer end of the spring being Joined to an upstanding arm ii on one end of an elongated arm 52 oscillatory about the axis of bearing 41 and having several bends 53, 64, 55 and 68, such member 62 extending through an aperture 51 in element 39 (Figure 5).

Part it constitutes a. handle by means of which an index 68, mounted on the member 62 and pro- Jecting up through an arcuate slot 59 through the plate 39, may be turned into register with the zero-graduation on a curved scale 1| (Figure 4) on the top of plate 39, the index 59 being normally maintained in adjusted zero position by a friction-spring 12 carried by the part 62 and 11 can also register with the same zero, and the two oppositely coiled springs 54 and 58 will oppose with equal force the movement of the pointer in either of its opposite directions of rocking movement.

Whereas, the appliance so far described can be made to register the amount of unbalance in the revolving rotor, the preferred construction embodies other features and properties.

Accordingly, adjacent to scale 1|, the plate 39 is provided with a slot 19 curved in conformity with the curvature of the scale which, of course, agrees with the path of travel of the end 19 of the pointer 11 which is just above the slot, and, directly beneath and in register with the slot 18, is a gas-filled or neon tube 8| (Figure and its electric-terminal 92 (Figure 4).

In addition, as shown in Figures 1, 2 and 3, the appliance directly above the axis of rotor 2| is supplied with a stroboscopic-light 83 and its associated fixed pointer or index 84 and the rotor, just beneath the pointer, is fitted with a temporary, circular, peripheral, numerically graduated band 85 in the present case with twenty graduations.

This entire assembly designated as 80 in Figures 2, 3, 4, 5 and 6, as has been indicated, is mounted on one of the bearing-supports 29, as portrayed in Figures 1, 2 and 3, so that the relatively-small, vibratory motion about the axis of the aligned pivots 43 and 44 of the adjustable mass-system 48, 49, 5| is mechanically magnified by means of the gear-train 42, 13 to cause comparatively greater motion of pointer 11 in connection with the graduated scale 1|, th spiral springs 54 and 58 normally holding pointer end 19 at zero.

With this complete assembly mounted as indicated on the balance-testing machine, vibration caused by unbalance in the revolving rotor oscillates the assembly and pointer 11, 19 will have amplified motion over scale 1| either side of zero, in phase with and proportional to unbalance in a selected transverse correction-plane of the rotor as indicated more fully hereinafter.

If a self-excited electric-pulse generator be used to flash the stroboscopic-light 83 (Figures 1, 2 and 3) and at the same time flash the gasfllled tube 8| (Figures 4 and 5) at a rate equal to the R. P. M. of the rotor, a numeral on numberband 85 will be apparently stationary opposite index-pointer 84 and the image of pointer-tip 19 may be viewed as stationary above the opening 19 If the speed of flash be now changed by ad- Justing potentiometer 99 of Fig. 7 to a synchronous rate at a time when the pointer-image is at the end of its travel, the maximum amplitude of unbalance will be indicated on scale 1|, and the stroboscopic-light 83 and its pointer M will indicate the unbalance position on number-band 85, and, as pointer 11--19 is oscillating in phase with the unbalance-it necessarily follows that when such pointer is at the end of its travel so also is the vibration amplitude of the rotor at its maximum displacement.

Therefore, if the pointer-image 19 is stopped at one end of its travel, the heavy unbalance point is at its maximum displacement point in the horizontal plane, and, ii the'pointer 19'is "stopped" at the opposite travel end, the'heavy unbalance point is at its maximum displacement in the opposite direction. v

Consequently, as the stroboscopic-light 83 and the gas-filled tube 8| flash simultaneously, the index located as shown will indicate the positions that the rotor must be in to correct for unbalance in the horizontal plane at a point such as the numeral 5 on number-band 95, while the graduation opposite the pointer-image of pointer 19 on scale 1| will indicate the value of unbalance.

A more precise method of use involves increasing the speed of fiash to twice the R. P. M.

of the motor so. that two pointer-images may be over gas-tube B as the speed of flash R. P. M. and

viewed at synchronism, then by slightly increasing or decreasing the flash-rate the pointer-images will travel away from and toward each other at the maximum position as shown in Fig. 4 where each image 96 and B1 of pointer 19 has reached its maximum travel to the right and to the left of zero which represent the total amplitude.

If now the flash-rate be adjusted until these two pointer-images 89 and B1 merge into one only, this will be at the center of amplitude or ance point is indicated directly opposite the index 84 on the number-band B5. Either the light point or heavy point of the rotor may be indicated as the pointer 19 will travel in one direction when the heavy point is up and in the opposite direction when the light point is up.

At 86 and 81 there are shown the two pointer end images as they appear when stopped at both ends of the pointer travel, and, in this case, the examination shown at zero would not be feasible until the two images were merged into one at zero at the flash rate adjustment.

The foregoing operations were based on manually adjusting the pulse-generator by potentiometer 89 of Fig. 7 to vary the rate of light-flash for the stroboscopic-light 83 and the gas-filled tube 9|.

Such electrical pulses need not be in any particular phase relation with the unbalance of the rotor so long as they occur at a rate equal to or double the R. P. M. of the rotor, as the pulsegenerator may be phase-shifted by adjusting potentiometer 99 of Fig. 7 to cause the observation of a single pointer image at the zero point of scale 1| in the case of the double flash-rate, indicative of the center of vibration amplitude position and phase-shifted to cause two pointerimages at the widest separation indicative of the imbalance amplitude value.

In the case of a single-pulse per revolution, the pulse may be phase-shifted to a point where the single pointer-image is at its extreme travel position which is indicative of vibration-amplitude, and the Position of unbalance may be observed on the number-band 99.

In every case, however, with any given value of uhbalance the instantaneous position of the pointer 19 is the criterion of the vibration-amplitude and unbalance-position and, as the balancetesting machine is operated at a speed far above the natural frequency of its suspension-system, and as the inertia-operated mass-system of Figures 4, and 6 is oscillating at a rate far above its natural frequency, the double amplitude of pointer 19 remains substantially constant for all operating speeds. Therefore, the indicating system is substantially independent of speed, both as to amplitude and position of unbalance, this being of the greatest importance as even the best motor-drive will have some speed-variation, whereas this system may be successfully and eiilciently operated at varying speeds.

Bearing in mind that the indicating mechanism referred to hereinbefore will always oscillate at a frequency equal to the rotor R. P. M. and not at any other rate, we will now turn to the flash-providing means which, as indicated, may operate either at the speedof the rotor or at twice that speed, this construction being shown in Figure 7.

This known system which includes the gasfllled tube BI and the stroboscopic-light 93 has a direct electric current source, not shown, such as batteries or a rectifier-system operating from A.-C. lines, the latter being used in practice and connected to the negative and positive terminals of the voltage divider 99 and 99.

Basically, the system consists of a self-excited oscillator 9| and 92 and is of the type known as a multivibrator which is capable of producing voltage pulses over a wide frequency range.

In such a circuit only one of the two tubes 9| and 92 are conducting at a time, the circuit constants determining whether one tube shall conduct for a longer time than the other, therefore, with symmetrical constants each tube conducts for 180 electrical degrees of each cycle, the potentiometer 99 of Fig. '7 controlling the frequency of a range of about ten to one.

The above two tube oscillator controls 93 and 94 which in turn trips or controls 95 and the stroboscopic-light 93. 95 discharges condenser 99 through spark-coil 91 flashing gas-tube 9|.

With both switches 99 and 99 open, both the gas-tube 9| and the stroboscopic-light 93 will flash each time 9| and 92 are energized. If, however, one of the switches 99 or 99 is closed the corresponding tube 93 or '94 will be prevented from operation and, therefore, the gas-tube and the stroboscope-light will flash at one-half the oscillatory frequency.

If the potentiometer 99 of Figure '7 be adjusted to flash the stroboscope-lamp 93 at a rate synchronous with the vibration of the unbalanced rotor and the voltage developed by the crystalgenerator IM, and mounted on one of the bearing members 29, or by other voltage-developing means, be applied to the input terminals I96 and I9! of the system portrayed in Figure '7, the oscillator will be held in step with the rotation of the rotor and then by the use of either one or both of the switches 98 or 99 one or two flashes per revolution may be obtained for the strobescope-light and the gas-filled tube.

The adjustment of oscillator frequency need not be exact as the voltage developed by the crystal-generator IN or other means will pull the oscillator into step with the rotation of the rotor after which phase adjustment may be made with the potentiometer 99.

The synchronizing voltage obtained from the crystal or other generator will keep the osciila-' tor in step at either one or two flashes per revolution because of the self-running or self-excited feature of the oscillator and its symmetrical electrical constants, and, therefore, the speed of the rotor may vary but the oscillator will keep in step therewith.

There are other types of pulse-generators or as they are sometimes called trigger-circuits" that operate on input signals or input voltage, such as from the crystal-generator and are responsive to both the positive and negative halfcycles, producing two pulses per cycle, such a trigger-circuit needing only the introduction of a rectifier to cause it to trip at one pulse per cycle, selecting either the positive or the negative half-cycle by switch means.

The circuit described and shown will function as required furnishing the desired single or multiple-flash rate, either with or without the synchronizing potential from the crystalgenerator.

Attention is directed to the fact that the present invention includes the important improvement which exists in the present balancing appliance, namely the feature of using the electrical impulse from some device, such as the crystal-generator |9|, which is adapted to receive oscillation or vibration, but not rotation.

In the past many balance-testing machines have used some rotational device attached for rotation with the rotor undergoing test to obtain electrical contact closings or to generate a voltage of the same frequency as the rotor, such as shown in Figures 3, 4 and 5 of the United States Patent No. 2,349,530 wherein the cam actuates the contact points through rotation. The present device eliminates all rotational parts and in their place there has been provided the inertia-operated oscillation-driven device, in this case, the crystal-generator |9l.

As illustrated most clearly in Figure 3, a piezoelectric crystal generator |||I referred to above is fixedly mounted on a vertically-depending portion I92 of the vibratory rotor-bearing member 29, such voltage-generator IM and its mounting being offset to the left from the vertical plane through the axis of the rotor-shaft 28.

Such crystal-generator is of the known type used, for example, in phonograph-record pickup work wherein the needle is demountably held in the generator and the vibrations of the needle by the record are transmitted to the crystal placing the latter under varying strains which produce the required changing voltages.

In this case, however, the needle has been replaced by a small rod carrying a weight I93, the developed voltages being available through the two terminal wires I94 and I95 associated with the crystals.

The value of the weight and the angle of mounting are not important or critical, one essential thing being to attach the generator to the vibrating part of the machine so that the weight will tend to remain stationary while the crystal will flex and generate a voltage which 7 is, of course, of the same frequency as the R. P. M. of the rotor, this factor being the only essential requirement of the generator which might be aptly characterized as an impulse timing unit.

The oil-center location of the generator is employed as there exists the remote possibility that the center-of-percussion point, or point of zero motion, might be in the bearing on the vertical center plane, whereas it is impossible for such a point to occur at either side of such plane.

It will be readily perceived that, if the centerof-percussion point of zero motion existed I through the center of the generator, there would be-no motion to cause the crystal to flex and, therefore, no voltage developed, but this cannot occur with the generator away from the center plane where it is impossible to encounter the percussion center.

The single weight employed is simply of any value of mass to cause the crystal to flex and generate any value of voltage for synchronizing purposes.

Preliminary to the testing of the unknown balance characteristics of rotors II, a like rotor is first balanced by trial and error, after which a known unbalance weight is aflixed thereto in the left-hand one of two initially-selected, transverse correction-planes 200 and 300 through such already balanced rotor which under those circumstances would be in the place of the rotor 2|, illustrated in Figures land 2, and during the rotation of such now unbalanced, but previously balanced, rotor the two weights 4! and 5| of the mass system 80 on the right-hand bearing member 29 are adjusted longitudinally with respect to one another on their common rod 48 to eliminate all oscillation thereof about the axis of the two aligned pivots 43 and 44 resulting in zero indication on the associated scale H and, after this condition has been established, such mass-assembly of the appliance 80 will respond to unbalance present in all transverse planes through the rotor except that in the left-hand correction-plane 200.

'When the meter gives a zero reading as set forth above, the inertia values of the two weights 49 and 5! are equal and there is, therefore, no tendency to move the pointer 11, 19, it being understood that when the meter indicates a value of unbalance, it is due to the fact that the two inertia forces of the two masses 48 and 5| are not the same and do not balance one another.

Then this unbalance weight may now be removed from the correction-plane 200 of the rotor and be applied to the rotor in the right-hand correction-plane 3M and the mass-assembly of the second indicating mechanism, characterized l8l in Figures 1, 2 and 3, is thereupon, during the rotation of the now unbalanced rotor, adjusted to zero response and this mass-assembly of the appliance IBI will now respond to unbalance in any transverse plane through the rotor except any in the right-hand correction-plane 300.

Now the mass-assembly of 'the indicatingmechanism 80 will respond proportionately to any unbalance attached in the right-hand correctionplane 300 and the mass-assembly of the indicatormechanism Ill will respond proportionately to any unbalance weight attached to the rotor in the left-hand correction-plane 200, and, therefore, by the employment of known unbalance weights in the planes referred to, the scales II of both indicators may be calibrated in amounts of unbalance.

Thereafter, any number of. similar or comparable rotors of unknown unbalance properties may be tested without further mass-system adjustment and the scales of the two appliances IBI and I! will, show the amounts of unbalance in the two planes 200 and 300, which information will render the balancing of the rotor a matter of ease and-convenience, the angular position of application of added weight or reduced weight being shown by the cooperating stroboscopic-light and its graduated band 86 as hereinbefore set forth.

Those acquainted with this art will readily understand that this invention, as defined by the appended claims, is not necessarily limited and restricted to the precise and exact features of detail set forth, and that reasonable modifications may be resorted to without departure from the heart and essence of the invention and without the loss or sacrifice of any of its material benefits and advantages.

Whereas herein a pair of weights 48 and ll of different values have been described as adjustable relative to one another on the pivoted threaded rod 48 common to both, it is to be understood that any equivalent mechanical structure may be substituted therefor, as for example two weights of equal value, or a mere single rod without any added weights thereon provided such rod is of proper weight and length and is adjustable lengthwise with relation to the pivot so that the weights of the portions of the rod on the opposite sides of the pivot are unequal in amounts to accomplish the stated results.

We claim:

1. In a balance-indicator, for use on a balancetesting machine in which the revolving rotor undergoing test vibrates horizontally by its unbalance, the novel combination of a mounting for attachment to said machine to be vibrated in consonance with the unbalance vibration of the rotor, a support having a vertical axis carried on said mounting, a pair of inertia-weights mounted on a horizontal rod on said support on opposite sides of its axis with manual adjustment toward and from one another on said rod and adapted to oscillate said support by the action of the rotor unbalance on the weights, means displaying a scale graduated in opposite directions from an intermediate zero-graduation, a movable pointer coacting with said scale, mechanical means to actuate said pointer by the oscillation of said support, and opposed yielding means to maintain said rod and its weights in neutral position parallel to the axis of the revolving rotor and with the pointer at zero-graduation of the scale when not subjected to rotor unbalance.

2. The balance-indicator set forth in claim 1, in which said inertia-weights are of different values.

3. The balance-indicator set forth in claim 1, including in addition an intermittently actuated light-flash means to illuminate said pointer automatically in synchronism with the unbalanced rotor vibration.

4. The balance-indicator set forth in claim 1,

' including in addition a light-flash means to illuminate said pointer automatically, and manually controlled means to produce said flashes at different periodicities including one that is in synchronism with the unbalanced rotor vibration.

5. The balance-indicator set forth in claim 1, including in addition a light-flash means to illuminate said pointer, and means to produce a flash canes thereby automatically for each revolution of the s. The balance-indicator set forthin claim 1,

8. The balance-indicator set forth in claim 1,

including in addition a light-flash means to illuminate said pointer, and means to produce said flashes thereby automatically coincident with the locations of the pointer at both of its opposite extreme positions.

9. The balance-indicator set forth in claim 1,

including in addition a light-flash means to illuminate said pointer, and means to produce said flashes thereby automatically coincident with the locations of the pointer at both of its extreme positions and manually adjustable to cause said flashes to occur automatically at the zero graduation positions of the pointer.

10. A balance-indicator, for use on a balancetesting machine in which the revolving rotor undergoing test is mounted for vibration horizontally by its unbalance and in which such rotor is provided with means displaying a rotary, circular graduated scale and with a stroboscopiclight and its cooperative index, said balanceindicator including the novel combination of a mounting for attachment to said machine to be vibrated in consonance with the unbalance vibration of the rotor, a support having a vertical axis carried on said mounting, a pair of inertiaweights mounted on a horizontal rod on said support on opposite sides of its vertical axis with manual adjustment toward and from one another on said rod and adapted to oscillate said support by the action of the rotor unbalance on the weights, means displaying a second scale on said mounting graduated in opposite directions from an intermediate zero-graduation, a movable pointer coacting with said second scale, mechanical means to actuate said pointer by the oscillation of said support, and opposed yieldable means to maintain said horizontal rod and its intertia weights in neutral position parallel to the axis of the revolving rotor and with the pointer at zero graduation of the second scale when not subjected to rotor unbalance, a light-flash means to illuminate said pointer, and means to produce automatically simultaneous flashes of said lightflash means and of said stroboscopic-light.

11. The balance-indicator set forth in claim 1, including in addition a light-flash means to illuminate said pointer automatically and an electric current generator energized by the vibration of the unbalanced revolving rotor determining the timed intervals of said light-flashes.

12. The balance-indicator set forth in claim 10, including an electric-current generator energized by the vibration of the unbalanced revolving rotor determining the timed periods of the simultaneous flashes of said light-flash means.

13. The balance-indicator set forth in claim- 1, including in addition a light-flash means to illuminate said pointer. means to produce said flashes automatically at timed intervals, and a non-rotary electric current generator energized l0 rotor determining the timed intervals oi said light-flashes.

14. The balance-indlcatorset forth in claim 10, including a non-rotary electric current generator energized by the vibration of the unbalanced revolving rotor determining the timed intervals of the means toproduce automatically the simultaneous flashes or said light-flash means and of said stroboscopic-light.

15. Inc. balance-indicator, {or use on u balonce-testing machine in which the revolving rotor undergoing test vibrates in a given axial plane by reason of its unbalance, the combination of a mounting for attachment to said machine to be vibrated in consonance with the unbalance vibration of the rotor, means carried by said mounting and providing 4 P votal vertical axis extending transverse to the direction of the vibration of the rotor in said axial plane, inertiaweight means carried by said first named means and having a moment relative to said pivotal axis with its center of mass oflset from said axis in a. direction at an angle to the direction of said vibrations and at an angle to a plane which includes said vertical axis and which is perpendicular to the axis-,0] said rotor whereby said inertia-weight means oscillates about said axis free from gravitational interference, means to adjust the eflective moment of said inertiaweight means, means on said mounting displaying a scale graduated in opposite directions from an intermediate zero-graduation, a movable pointer coacting with said scale, means to actuate said pointer in response to the oscillation of said inertia-weight means, and opposed sprin means to bias said inertia-weight means to a neutral static position with the pointer at zerograduation on the scale.

. 16.1n combination with the balance-indicator of claim 15, a light-flash means disposed to illuminate said scale and pointer, and adjustable means to supply current to said light-flush means and produce flashes thereof at an adjustable frequency related to the frequency of oscillation of said inertia-weight means and pointer whereby two images of said pointer may be seen at spaced positions on said scale and said images may be merged into a single image at the center of pointer oscillation.

17. A balance-indicator, for use on a balance testing machine in which the revolving rotor undergoing test is mounted for vibration in a given axial plane by reason of its unbalanceand in which such rotor is provided with means displaying a. rotary circular graduated scale to cooperate with a stroboscopic-light and it cooperative index, said balance-indicator includin the combination of a mounting for attachment to said machine to be vibrated in consonance with the unbalance vibration of the rotor, means carried by said mounting and providing a. pivotal vertical axis, inertia-weight means carried by said first named means and having a moment relative to said pivotal axis with its center of mass ofiset from said axis in a direction at an angle to the direction of said vibrations and at an angle to a plane which includes s tlid vertical axis and which is perpendicular to e axis of said rotor whereby said inertia-weig it means oscillate about said axis free from gravitational interference, means to adjust the eflective moment of said inertia-weight means, means on said mounting displaying a second scale graduated in opposite directions from an intermediate zerograduation, a movable pointer coocting with said IRA A. WEAVER. CLYDE H. PHELPS.

Belerences emu m the me or this patent or the original patent UNITED STATES PATENTS Number Name I Date -McGa11 Sept. 6, 1927 Kimball, Jr., et a1. Sept. 10, 1929 Lundgren Mar. 24, 1931 Davey Mar. 6, 1934 Kolesnlk Nov. 10, 1942 Buchanan Nov. 24, 1942 Sihvonen et a1 Aug. 14. 1945 Annie Aug. 14, 1945 Hope Aug. 26, 1947 

